Method for selectively modifying spacing between pitch multiplied structures

ABSTRACT

Methods for circuit material processing are provided. In at least one such method, a substrate is provided with a plurality of overlying spacers. The spacers have substantially straight inner sidewalls and curved outer sidewalls. An augmentation material is formed on the plurality of spacers such that the inner or the outer sidewalls of the spacers are selectively expanded. The augmentation material can bridge the upper portions of pairs of neighboring inner sidewalls to limit deposition between the inner sidewalls. The augmentation material is selectively etched to form a pattern of augmented spacers having a desired augmentation of the inner or outer sidewalls. The pattern of augmented spacers can then be transferred to the substrate through a series of selective etches such that features formed in the substrate achieve a desired pitch.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.13/238,192, filed Sep. 21, 2011, entitled METHOD FOR SELECTIVELYMODIFYING SPACING BETWEEN PITCH MULTIPLIED STRUCTURES, which is acontinuation of U.S. patent application Ser. No. 12/053,513, filed Mar.21, 2008, entitled METHOD FOR SELECTIVELY MODIFYING SPACING BETWEENPITCH MULTIPLIED STRUCTURES.

Reference to Related Applications

This application is related to the following: U.S. patent applicationSer. No. 10/934,778 to Abatchev et al., filed Sep. 2, 2004 (AttorneyDocket No. MICRON.294A); U.S. patent application Ser. No. 11/214,544 toTran et al., filed Aug. 29, 2005 (Attorney Docket No. MICRON.316A); andU.S. patent application Ser. No. 11/959,409 to Tran et al., filed Dec.18, 2007 (Attorney Docket No. MICRON.394A).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the fabrication of integratedcircuits and electronic devices and, more particularly, to fabricationmethods and related structures.

2. Description of the Related Art

As a consequence of many factors, including demand for increasedportability, computing power, memory capacity and energy efficiency,integrated circuits are constantly being reduced in size. The sizes ofthe constituent features that form the integrated circuits, e.g.,electrical devices and interconnect lines, are also constantly beingdecreased to facilitate this size reduction.

The trend of decreasing feature size is evident, for example, in memorycircuits or devices such as dynamic random access memories (DRAMs),flash memory, static random access memories (SRAMs), ferroelectric (FE)memories, etc. To take one example, DRAM typically includes millions orbillions of identical circuit elements, known as memory cells. A memorycell typically consists of two electrical devices: a storage capacitorand an access field effect transistor. Each memory cell is anaddressable location that may store one bit (binary digit) of data. Abit may be written to a cell through the transistor and may be read bysensing charge in the capacitor.

In another example, flash memory typically includes billions of flashmemory cells containing floating gate field effect transistors that canretain a charge. The presence or absence of a charge in the floatinggate determines the logic state of the memory cell. A bit may be writtento a cell by injecting charge to or removing charge from a cell. Flashmemory cells may be connected in different architecture configurations,each with different schemes for reading bits. In a “NOR” architectureconfiguration, each memory cell is coupled to a bit line and may be readindividually. In a “NAND” architecture configuration, memory cells arealigned in a “string” of cells, and an entire bit line is activated toaccess data in one of the string of cells.

In general, by decreasing the sizes of the electrical devices thatconstitute a memory cell and the sizes of the conducting lines thataccess the memory cells, the memory devices may be made smaller.Additionally, storage capacities may be increased by fitting more memorycells on a given area in the memory devices.

The concept of pitch may be used to describe one aspect of the sizes offeatures in an integrated circuit such as a memory device. Pitch isdefined as the distance between identical points in two neighboringfeatures, such as features in an array, which are typically arranged ina repeating pattern. These features are typically defined by spacesbetween adjacent features, which spaces are typically filled by amaterial, such as an insulator. As a result, pitch may be viewed as thesum of the width of a feature and of the width of the space on one sideof the feature separating that feature from a neighboring feature. Itwill be appreciated that the spaces and features, such as lines,typically repeat to form a repetitive pattern of spacers and features.

Critical dimension (CD) is another term used to describe the sizes offeatures. The critical dimension is the smallest dimension of a featurein a particular circuit or masking scheme. Controlling the CD of certainstructures, such as shallow trench isolation (STI) structures, duringintegrated circuit fabrication helps to facilitate the continued sizereduction of integrated circuits by, e.g., ensuring predictable circuitperformance.

The continual reduction in feature sizes places ever greater demands onthe techniques used to form the features. For example, photolithographyis commonly used to pattern features, such as conductive lines, inintegrated circuit fabrication. However, due to factors such as optics,light or radiation wavelength and available photoresist materials,photolithography techniques may each have a minimum pitch or criticaldimension below which a particular photolithographic technique cannotreliably form features. Thus, the inherent limitations ofphotolithographic techniques are obstacles to continued feature sizereduction.

“Pitch doubling,” which is also referred to as “pitch multiplication,”is one proposed method for extending the capabilities ofphotolithographic techniques beyond their minimum pitch. A pitchmultiplication method is illustrated in FIGS. 1A-1F and described inU.S. Pat. No. 5,328,810, issued to Lowrey et al. With reference to FIG.1A, a pattern of lines 10 is photolithographically formed in aphotoresist layer, which overlies a layer 20 of an expendable material,which in turn overlies a substrate 30. As shown in FIG. 1B, the patternin the photoresist layer is transferred to the layer 20, thereby formingplaceholders, which are also referred to herein as mandrels, 40. Thephotoresist lines 10 are stripped and the mandrels 40 are etched toincrease the distance between neighboring mandrels 40, as shown in FIG.1C. A layer 50 of spacer material is subsequently deposited over themandrels 40, as shown in FIG. 1D. Spacers 60 are then formed on thesides of the mandrels 40. The spacer formation can be accomplished bypreferentially etching the spacer material from the horizontal surfaces70 and 80, as shown in FIG. 1E. The remaining mandrels 40 are thenremoved, leaving behind only the spacers 60, which together act as amask for patterning, as shown in FIG. 1F. Thus, where a given pitchpreviously included a pattern defining one feature and one space, thesame width now includes two features and two spaces, with the spacesdefined by the spacers 60.

While the pitch is actually halved in the example above, this reductionin pitch is conventionally referred to as pitch “doubling,” or, moregenerally, pitch “multiplication.” Thus, conventionally,“multiplication” of pitch by a certain factor actually involves reducingthe pitch by that factor. The conventional terminology is retainedherein.

While allowing for smaller critical dimensions and pitch, pitchmultiplication faces continuing development as new challenges emerge, asthe requirements of integrated circuit fabrication change. Accordingly,there is a constant need for methods and structures for forming smallfeatures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1F are schematic, cross-sectional side views of a sequence ofmasking patterns for forming conductive lines, in accordance with aprior art pitch multiplication method.

FIG. 2 is a schematic top plan view of a partially formed integratedcircuit, in accordance with some embodiments of the invention.

FIGS. 3A and 3B are schematic cross-sectional side and top views of thepartially formed integrated circuit of FIG. 2, in accordance with someembodiments of the invention.

FIGS. 4A and 4B are schematic cross-sectional side and top plan views ofthe partially formed integrated circuit of FIGS. 3A and 3B after forminglines in a photoresist layer in an array region of the integratedcircuit, in accordance with some embodiments of the invention.

FIGS. 5A and 5B are schematic cross-sectional side and top plan views ofthe partially formed integrated circuit of FIGS. 4A and 4B afterwidening spaces between lines in the photoresist layer, in accordancewith some embodiments of the invention.

FIG. 6 is a schematic, cross-sectional side view of the partially formedintegrated circuit of FIGS. 5A and 5B after depositing a layer of aspacer material, in accordance with some embodiments of the invention.

FIGS. 7A and 7B are schematic, cross-sectional side and top plan viewsof the partially formed integrated circuit of FIG. 6 after a spaceretch, in accordance with some embodiments of the invention.

FIGS. 8A and 8B are schematic, cross-sectional side views of thepartially formed integrated circuit of FIGS. 7A and 7B after removing aremaining portion of the temporary layer to leave a pattern offree-standing spacers, in accordance with some embodiments of theinvention.

FIGS. 9A and 9B are schematic, cross-sectional side views of thepartially formed integrated circuit of FIGS. 8A and 8B after depositingaugmentation material between and over the spacers, in accordance withsome embodiments of the invention.

FIG. 10 is a scanning electron micrograph showing the spacers formedafter a spacer etch, according to some embodiments of the invention.

FIG. 11 is a scanning electron micrograph showing the spacers afteraugmentation material deposition and the formation of an augmentationmaterial bridge between spacers, according to some embodiments of theinvention.

FIGS. 12A and 12B are schematic, cross-sectional side views of thepartially formed integrated circuit of FIGS. 9A and 9B after etching theaugmentation material, in accordance with some embodiments of theinvention.

FIGS. 13A and 13B are schematic, cross-sectional side views of thepartially formed integrated circuit of FIGS. 12A and 12B after forminganother mask pattern overlying the substrate and before transferring thespacer pattern to the substrate, in accordance with some embodiments ofthe invention.

FIGS. 14A and 14B are schematic, cross-sectional side views of thepartially formed integrated circuit of FIGS. 13A and 13B where the maskpattern is transferred to a planarization layer on the same level as thespacer pattern in preparation for transfer to the underlying hard masklayer, in accordance with some embodiments of the invention.

FIGS. 15A and 15B are schematic, cross-sectional side views of thepartially formed integrated circuit of FIGS. 14A and 14B after forming acombined pattern defined by a patterned planarization material and theaugmented spacers to an underlying hard mask layer, in accordance withsome embodiments of the invention.

FIGS. 16A and 16B are schematic, cross-sectional side views of thepartially formed integrated circuit of FIGS. 15A and 15B aftertransferring the combined pattern to a primary mask layer, in accordancewith some embodiments of the invention.

FIGS. 17A and 17B are schematic, cross-sectional side views of thepartially formed integrated circuit of FIGS. 16A and 16B aftertransferring the combined pattern to the underlying substrate, inaccordance with some embodiments of the invention.

FIGS. 18A and 18B are schematic, cross-sectional side and top views ofthe partially formed integrated circuit of FIGS. 17A and 17B aftertransferring the pattern into the substrate and removing hard masklayers overlying the substrate, in accordance with some embodiments ofthe invention.

FIGS. 19 is a scanning electron micrograph showing features formed in asubstrate, in accordance with some embodiments of the invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

A challenge in current pitch multiplication structures is achieving adesired balance between the inner and outer spaces. The inner and outerspaces are typically formed through a process of forming spaced apartmandrels, depositing a spacer material layer on the mandrels,directionally etching the spacer material layer, and removing themandrels. This process results in spacers with substantially straightinner space walls, which were alongside the mandrels, and curved outerspace walls on the side of the spacers without mandrels. As used herein,inner and outer space walls, which can also be referred to as sidewalls,can refer to opposite sides of the same spacer. Facing adjacent straightinner walls define the inner space and facing adjacent curved outerwalls define the outer space. The spacers are used as a mask to etchunderlying materials, such as hard masks and substrates. As a result,the spacing between spacers determines the spacing between later-formedfeatures in the hard masks and substrates. Variations in processconditions and chemistries can cause the inner and outer spaces to beunbalanced, such that one is larger than the other. It will beappreciated that improving the uniformity between the inner and outerspace is beneficial for improving the alignment of features formed usingthe spacers and for improving the reliability of the final productformed by the process. It has been believed that once the spacingbetween the free-standing spacers has been formed by the spacerformation process, the spacing cannot be selectively altered since thesides of the spacers are equally exposed to process gases.

Advantageously, some embodiments of the invention allow the inner orouter spaces to be selectively changed by laterally expanding the inneror outer sidewalls of spacers. Certain embodiments of the inventionemploy material deposition and/or etches that are selective with regardto the inner and outer spaces or walls.

In pitch multiplication, spacers typically have a straight inner walland a curved outer wall due to formation of the spacers by etching alayer of spacer material. The curved outer wall is formed by greaterexposure of the outer wall to etchant than the inner wall, which istypically adjacent to a mandrel that protects the inner wall from theetchant to a degree. Deposition and etching of an augmentation materialon the spacers can be used to selectively grow or reduce the inner orouter space. Deposited material at the tops of the neighboring spacerstend to bridge together, e.g., seal, during the deposition such that thedeposition in the inner space is blocked or slowed down but thedeposition in the outer space is not similarly blocked or slowed down.As a result, the thickness of the deposited material is differentbetween the inner to the outer spaces after the deposition andfacilitates selective modifications of the widths of the inner and outerspaces. In some embodiments, the deposited material is a polymer, suchas an organic polymer.

In certain embodiments where reduction of the outer space is desired,after deposition of the augmentation material, an etch at a high biaspower is used. The etch is preferably an anisotropic etch at a biaspower that is sufficiently high to remove the top bridge of material andthe deposited augmentation material in the inner space. Since the innerspace is not as heavily deposited as the outer space due to formation ofthe bridge between neighboring pairs of spacers limiting additionaldeposition, the inner space is etched more quickly during the etch.Therefore, the etch maintains the inner space substantially as it wasbefore the deposition of augmentation material and helps to reduce theouter space since some deposited augmentation material still remains onthe outer wall of the spacer, due to the higher levels of depositedmaterial on the outer wall.

In certain embodiments where reduction of the inner space is desired,after deposition of the augmentation material, an etch at a relativelylow bias power is used to etch the deposited augmentation material. Theetch is preferably an anisotropic etch performed at a sufficiently lowpower to leave deposited material, which can also be referred to asfooters, at corners in the inner space, the corners defined by the innersidewall and an underlying material. While the invention is not limitedby theory, because the inner sidewall is straight and the outer space isrelatively widely open due to the curved outer sidewall, it is believedthat this etching is more isotropic in the inner space but moreanisotropic in the outer space. It is believe the relatively low biaspower, in conjunction with the relatively narrow inner space, reducesthe directionality of etchant species in the inner space while therelatively widely open outer space facilitates the directional movementof etchant species. The result of this differential etch behavior isthat the outer sidewalls defining the outer space is relatively straightwhile the bottom of the inner space is rounded and has footers ofdeposited augmentation material on each sidewall. After the etch of theaugmentation material, a pattern transfer etch of material underlyingthe spacers is applied. This pattern transfer etch has a highselectivity for the underlying material relative to the augmentationmaterial. The rounded inner space bottom reduces the available openingfor etching the underlying material, thereby narrowing the inner spacefor the pattern transfer. As a result, the pattern transferred to theunderlying material has features corresponding to an inner space whichis narrower than that formed initially after the spacer formation etch.

Reference will now be made to the Figures, wherein like numerals referto like parts throughout. It will be appreciated that these Figures arenot necessarily drawn to scale. Moreover, it will be appreciated thatonly a limited number of features, including mask features and etchedfeatures such as bit lines, word lines, spacers, and memory blocks areillustrated for ease of discussion and illustration. Different numbersof and/or positions for these features can be provided in someembodiments.

In a first phase of some embodiments of the invention, mask features areformed by pitch multiplication.

FIG. 2 shows a top view of a portion of a partially fabricatedintegrated circuit 100. While the embodiments of the invention may beused to form any integrated circuit and may be applied to form masks forpatterning various substrates, they may particularly advantageously beapplied to form devices having arrays of electrical devices, includingmemory cell arrays for volatile and non-volatile memory devices such asDRAM, ROM or flash memory, including NAND or NOR flash memory, orintegrated circuits having logic or gate arrays. For example, the logicarray may be a field programmable gate array (FPGA) having a core arraysimilar to a memory array and a periphery with supporting logics.Consequently, the integrated circuit 100 may be, e.g., a memory chip ora processor, which may include both a logic array and embedded memory,or any other integrated circuit having a logic or a gate array.

With continued reference to FIG. 2, a central region 102, which will bereferred to hereinafter by example as the “array,” is surrounded by aperipheral region 104, which is often referred to hereinafter as the“periphery.” It will be appreciated that, in a fully formed integratedcircuit, such as a memory device, the array 102 will typically bedensely populated with electrically conductive line and electricaldevices, including transistors and/or capacitors. In a memory device,the electrical devices form a plurality of memory cells, which may bearranged in a regular grid pattern at the intersection of access linesand data lines, which are conventionally referred to in the industry as“word” lines and “bit” lines, respectively. Desirably, pitchmultiplication may be used to form features such as rows/columns oftransistors and/or capacitors in the array 102, as discussed herein. Onthe other hand, the periphery 104 typically comprises features largerthan those in the array 102. Conventional photolithography, rather thanpitch multiplication, is typically used to pattern features, such aslogic circuitry, in the periphery 104, because the geometric complexityof logic circuits located in the periphery 104 makes using pitchmultiplication difficult, whereas the regular grid typical of arraypatterns is conducive to pitch multiplication. In addition, some devicesin the periphery require larger geometries due to electricalconstraints, thereby making pitch multiplication less advantageous thanconventional photolithography for such devices. In some cases, theperiphery 104 may contain patterns/circuits defined by both conventionallithography and pitch multiplication. In addition to possibledifferences in relative scale, it will be appreciated by the skilledartisan that the relative positions, and the number of periphery 104 andarray 102 regions in the partially fabricated integrated circuit 100 mayvary from that depicted.

FIG. 3A shows a cross-sectional side view of the partially formedintegrated circuit 100 and FIG. 3B shows a top plan view of theintegrated circuit 100. With reference to FIG. 3A various masking layers120-140 are provided above a substrate 110. The layers 120-140 will beetched to form a mask for patterning the substrate 110, as discussedbelow. In the illustrated embodiment, a selectively definable layer 120overlies a hard mask layer 130, which can also be referred to as an etchstop, which overlies a primary mask layer 140, which overlies thesubstrate 110 to be processed (e.g., etched) through a mask.

The materials for the layers 120-140 overlying the substrate 110 arechosen based upon consideration of the chemistry and process conditionsfor the various pattern forming and pattern transferring steps discussedherein. Because the layers between the topmost selectively definablelayer 120 and the substrate 110 function to transfer a pattern derivedfrom the selectively definable layer 120 to the substrate 110, thelayers 130-140 between the selectively definable layer 120 and thesubstrate 110 are chosen so that they may be selectively etched relativeto other exposed materials. It will be appreciated that a material isconsidered selectively, or preferentially, etched when the etch rate forthat material is at least about 2-3 times greater, at least about 10times greater, at least about 20 times greater, or at least about 40times greater than that for surrounding materials. Because a goal of thelayers 120-130 overlying the primary hard mask layer 140 is to allowwell-defined patterns to be formed in that layer 140, it will beappreciated that one or more of the layers 120-130 may be omitted orsubstituted if suitable other materials, chemistries and/or processconditions are used. For example, where the substrate is relativelysimple and may be selectively etched relative to the hard mask layer130, the primary mask layer 140 may be omitted and patterns may betransferred directly to the substrate using the hard mask layer 130.

With continued reference to FIG. 3A, the selectively definable layer 120is photodefinable in some embodiments, e.g., formed of a photoresist,including any photoresist, including any positive or negativephotoresist, known in the art. For example, the photoresist may be anyphotoresist compatible with 157 nm, 193 nm, 248 nm or 365 nm wavelengthsystems, 193 nm wavelength immersion systems, extreme ultravioletsystems (including 13.7 nm wavelength systems) or electron beamlithographic systems. In addition, maskless lithography, or masklessphotolithography, may be used to define the selectively definable layer120. Examples of photoresist materials include argon fluoride (ArF)sensitive photoresist, i.e., photoresist suitable for use with an ArFlight source, and krypton fluoride (KrF) sensitive photoresist, i.e.,photoresist suitable for use with a KrF light source. ArF photoresistsare used with photolithography systems utilizing relatively shortwavelength light, e.g., 193 nm wavelength light. KrF photoresists areused with longer wavelength photolithography systems, such as 248 nmsystems. In other embodiments, the layer 120 and any subsequent resistlayers may be formed of a resist that may be patterned by nano-imprintlithography, e.g., by using a mold or mechanical force to pattern theresist.

In some embodiments, the material for the hard mask layer 130 comprisesan inorganic material. Materials for the hard mask layer 130 includesilicon oxide (SiO₂), silicon or an anti-reflective coating (ARC), suchas a silicon-rich silicon oxynitride, a silicon-rich nitride, or a filmthat has the desired etch selectivity relative to the spacers 175 orother exposed materials (FIG. 7A). In some embodiments, a Si, O, andN-containing spin-on hard mask with, for example, a 17% or a 43% Sicontent may be used for the layer 130, which may be part of amulti-layer resist (MLR). The hard mask layer 130 may also includecombinations of layers of materials, e.g., a bottom anti-reflectivecoating (BARC) over a dielectric anti-reflective coating (DARC). Forease of description, in the illustrated embodiment, the hard mask layer130 is an anti-reflective coating, such as DARC. It will be appreciatedthat using ARCs for the hard mask layer 130 may be particularlyadvantageous for forming patterns having pitches near the resolutionlimits of a photolithographic technique. The ARCs can enhance resolutionby minimizing light reflections, thus increasing the precision withwhich photolithography can define the edges of a pattern.

With continued reference to FIG. 3A, embodiments of the invention mayutilize the primary masking layer 140 to facilitate pattern transfer toa substrate. As noted above, in common methods of transferring patterns,both the mask and the underlying substrate are exposed to etchant, whichmay wear away a mask before the pattern transfer is complete. Thesedifficulties are exacerbated where the substrate comprises multipledifferent materials to be etched. In some embodiments, the layer 140 isformed of a carbon-containing underlayer material.

In some other embodiments, due to its excellent etch selectivityrelative to a variety of materials, including oxides, nitrides andsilicon, the primary masking layer may be formed of amorphous carbon.The amorphous carbon layer may be formed by chemical vapor depositionusing a hydrocarbon compound, or mixtures of such compounds, as carbonprecursors. Carbon precursors may include propylene, propyne, propane,butane, butylene, butadiene and acetelyne. A method for formingamorphous carbon layers is described in U.S. Pat. No. 6,573,030 B1,issued to Fairbairn et al. on Jun. 3, 2003. In some embodiments, theamorphous carbon is a form of amorphous carbon that is highlytransparent to light and that offers further improvements for photoalignment by being transparent to the wavelengths of light used for suchalignment. Deposition techniques for forming such transparent carbon canbe found in, e.g., A. Helmbold, D. Meissner, Thin Solid Films, 283(1996) 196-203. In addition, the amorphous carbon may be doped as knownin the art.

It will be appreciated that the “substrate” to which patterns aretransferred may include a layer of a single material, a plurality oflayers of different materials, a layer or layers having regions ofdifferent materials or structures in them, etc. These materials mayinclude semiconductors, insulators, conductors, or combinations thereof.

With reference to FIGS. 4A and 4B, a pattern comprising spaces, such astrenches 122, which are delimited by photodefinable material features124, is formed in the photodefinable layer 120. The trenches 122 may beformed by, e.g., photolithography with 248 nm or 193 nm light, in whichthe layer 120 is exposed to radiation through a reticle and thendeveloped. After being developed, the remaining photodefinable material,photoresist in the illustrated embodiment, forms mask features such asthe illustrated lines 124 (shown in cross-section only).

The pitch of the resulting lines 124 is equal to the sum of the width ofa line 124 and the width of a neighboring space 122. To minimize thecritical dimensions of features formed using this pattern of lines 124and spaces 122, the pitch may be at or near the limits of thephotolithographic technique used to pattern the photodefinable layer120. For example, for photolithography utilizing 248 nm light, the pitchof the lines 124 may be about 100 nm. Thus, the pitch may be at theminimum pitch of the photolithographic technique and the spacer patterndiscussed below may advantageously have a pitch below the minimum pitchof the photolithographic technique. Alternatively, because the margin oferror for position and feature size typically increases as the limits ofa photolithographic technique are approached, the lines 124 may beformed having larger feature sizes, e.g., 200 nm or more, to minimizeerrors in the position and sizes of the lines 124.

As shown in FIGS. 5A and 5B, the spaces 122 are widened by etching thephotoresist lines 124, to form modified spaces 122 a and lines 124 a.The photoresist lines 124 are etched using an isotropic etch to “shrink”or trim those features. Suitable etches include etches using anoxygen-containing plasma, e.g., a SO₂/O₂/N₂/Ar plasma, a Cl₂/O₂/Heplasma or a HBr/O₂/N₂ plasma. The extent of the etch is selected so thatthe widths of the lines 124 a are substantially equal to the desiredspacing between the later-formed spacers 175 (FIG. 7), as will beappreciated from the discussion below. For example, the width of thelines 124 may be reduced from about 80-120 nm to about 30-70 nm or about50-70 nm. Advantageously, the width-reducing etch allows the lines 124 ato be narrower than would otherwise be possible using thephotolithographic technique used to pattern the photodefinable layer120. While the critical dimensions of the lines 124 a may be etchedbelow the resolution limits of the photolithographic technique, it willbe appreciated that this etch does not alter the pitch of the spaces 122a and lines 124 a, since the distance between identical points in thesefeatures remains the same.

Next, with reference to FIG. 6, a layer 170 of spacer material isblanket deposited conformally over exposed surfaces, including the hardmask layer 130 and the top and sidewalls of the primary mask layer 140.The spacer material may be any material that can act as a mask fortransferring a pattern to the underlying hard mask layer 130. The spacermaterial may be, without limitation, silicon, silicon oxide and siliconnitride. In the illustrated embodiment, the spacer material is siliconoxide, which provides particular advantages in combination with otherselected materials of the masking stack.

Methods for spacer material deposition include atomic layer deposition,e.g., using a self-limiting deposition with a silicon precursor and asubsequent exposure to an oxygen or nitrogen precursor to form siliconoxides and nitrides, respectively. In some embodiments, to form siliconoxide, a silicon halide, such as silicon hexachlorodisilane (HCD), isintroduced in alternating pulses with an oxygen precursor, such as H₂O.ALD can be performed at relatively low temperatures, e.g., under about200° C. or under about 100° C., which has advantages for preventingthermal damage to underlying carbon-based materials, such as photoresistand amorphous carbon layers. In other embodiments, chemical vapordeposition is used to deposit the spacer material, e.g., using O₃ andTEOS to form silicon oxide.

The thickness of the layer 170 is determined based upon the desiredwidth of the spacers 175 (FIG. 7A). For example, in some embodiments,the layer 170 is deposited to a thickness of about 20-80 nm or about40-60 nm to form spacers of roughly similar widths. The step coverage isabout 80% or greater and or about 90% or greater.

With reference to FIGS. 7A and 7B, the silicon oxide spacer layer 170 issubjected to an anisotropic etch to remove spacer material fromhorizontal surfaces 180 of the partially formed integrated circuit 100.

With reference to FIGS. 8A and 8B, the selectively definable layer 120is next removed to leave freestanding spacers 175. The selectivelydefinable layer 120 may be selectively removed using an organic stripprocess or various other etching processes.

Thus, pitch—multiplied mask features, the spacers 175, have been formed.In the illustrated embodiment, the spacers 175 form elongated loops andhave substantially parallel legs which are joined at their ends. Thepitch of the spacers 175 is roughly half that of the photoresist lines124 and spaces 122 (FIGS. 4A and 4B) originally formed byphotolithography, but the pitch can vary due to process deviations, asdiscussed herein. For example, where the photoresist lines 124 had apitch of about 200 nm, spacers 175 having a pitch of about 100 nm orless may be formed. It will be appreciated that because the spacers 175are formed on the sidewalls of the features, such as lines 124 b, thespacers 175 generally follow the outline of the pattern of lines 124 ain the modified photodefinable layer 120 a and, so, form a closed loopin the spaces 122 a between the lines 124 a.

Next, in a second phase of methods according to some embodiments of theinvention, augmentation material is deposited on the spacers 175 and theaugmentation material is etched to achieve a desired inner and outerspace balance.

With continued reference to FIGS. 8A and 8B, the freestanding spacers175 have straight inner walls 810 and curved outer walls 820. The spacebetween adjacent straight inner walls 810 defines the inner spaces 830.The space between adjacent outer walls 820 defines the outer space 840.Unless modified, imbalances between the widths of the inner space 830and the outer space 840 will typically result in the formation offeatures having non-uniform transfer of the spacer pattern to theunderlying substrate.

Process variations can cause the various imbalances between the widthsof the inner space 830 and the outer space 840. In certain embodiments,as shown in FIG. 8A, the outer spaces 840 are larger in dimension thanthe inner spaces 830. In other embodiments, as illustrated in FIG. 8B,the inner spaces 830 are larger in dimension with respect to the outerspaces 840.

Non-uniformities between the inner spaces 830 and the outer spaces 840can be measured by methods known in the art. For example, in the case ofa partially formed integrated circuit, a metrology tool can determinethe positions of the spacers 175 and the relative dimensions of theinner and outer spaces 830, 840. The imbalance with respect to thespacers 175 can then be adjusted using methods herein described.

With reference to FIGS. 9A and 9B, augmentation material, e.g., polymer,is deposited, e.g., by chemical vapor deposition, between and over thespacers 175. The deposition can be achieved in an etch chamber in whichprocess conditions are selected to cause deposition of material on thespacers 175. For example, in some embodiments, carbon-containing processgases such as CF₄ and CH₂F₂ are flowed into a reaction chamber having aRF power from about 300 W to about 1000 W and a RF bias voltage fromabout 150 V to about 500 V, with the ratio of CF₄:CH₂F₂ less than about2.

Since the spacers 175 are formed having a straight inner wall 810, whichis straight relative to the curved outer wall 820, the augmentationmaterial is deposited more thickly over the curved outer wall 820 due toits increased surface area. As used herein, “inner wall” and “outerwall” can refer to opposite sides of the same spacer 175. While theinvention is not limited by theory, it is believed that the preferentialdeposition on the curved outer wall, in conjunction with the abruptdrop-off of the relatively straight inner wall 810, cause the augmentedmaterial to begin bridging neighboring spacers 175 that have inner walls810 facing each other. The inner wall 810 receives less depositedmaterial due to its structural shape, but also because in someembodiments a bridge 910 may completely or partially form to block offany further deposition in between the inner walls 810.

FIG. 10 shows a scanning electron micrograph of spacers formed after aspacer etch. FIG. 11 shows the spacers after augmentation materialdeposition and the formation of an augmentation material bridge betweenspacers.

With reference again to FIG. 9A, augmentation material 920 is depositedonto the spacers 175 of FIG. 8A, in which the outer spaces 840 areenlarged with respect to the inner spaces 830. The augmentation material920 deposition occurs preferentially on the curved outer wall 820. Incertain embodiments, however, as the deposition progresses, thedeposited material begins to bridge the inner space 830. The inner space830 can become blocked by a bridge 910 forming between adjacent straightinner walls 810. This prevents the addition of further augmentationmaterial 920, resulting in the growth of the outer wall 820 andreduction in the outer space 840.

FIG. 9B illustrates the deposition of augmentation material 920 onto thespacers 175 of FIG. 8B, in which the inner spaces 830 are enlarged withrespect to the outer spaces 840. The augmentation material 920deposition also occurs preferentially on the curved outer wall 820, butin certain embodiments, due to the enlarged dimension of the inner space830 relative to the outer space 840, a greater degree of augmentationmaterial 920 deposition occurs on the inner walls 810 of the spacers 175than if the outer space 840 were larger than the inner space 830 (FIG.9A).

With reference to FIG. 12A, a high bias voltage anisotropic etch isapplied to etch the deposited polymer material. In one or moreembodiments, the etch has a low oxygen content, which has advantages forcontrollably combusting and removing carbon species without completelyremoving deposited polymer material. This etch provides a substantiallyvertical inner wall 810, and has a sufficiently high aggressiveness tosubstantially remove the deposited material on the inner wall 810, butpreserve a desired amount of deposited polymer on outer wall 820 toresult in a desired net decrease in the width of the outer space 840 dueto increasing the width of the spacers 175 on the outer wall 820 side ofthe spacers 175. In certain embodiments, the anisotropic etch mayinclude oxygen and a halide-containing etchant, the halides chosen fromthe group F, Cl, Br, and I. An example of a suitable etch chemistryincludes HBr, O₂, and He. It will be appreciated that suitable etchconditions, including RF conditions, will vary depending on variousfactors, including the etching system, chemistries, deposited materials,and etch conditions used. In some embodiments, N₂ and/or Ar can be addedto help stabilize the system. In some embodiments, the RF power is inthe range from about 200 W to about 1000 W and the RF bias voltage is inthe range from about 300 V to about 800 V.

FIG. 12B illustrates a low bias voltage anisotropic etch (e.g., a plasmaetch, which is often referred to as a “dry etch”) performed on thestructure of FIG. 8B where the inner space 830 was larger relative tothe outer space 840. This etch has a sufficiently low aggressiveness toremove the augmentation material more gradually in the corners of theinner space 830 and more aggressively at the midpoints of the innerspace or the outer spacer, such that footers 1210 remain on each side ofthe inner wall 810. These footers 1210 function to increase the basewidth of the inner wall 810, which decreases the effective width of theinner space 830 and narrows the exposed surface of the hard mask layer130.

The footers 1210 limit the etch of the underlying hard mask 130, whichthereby controls the transfer of the pattern from the combinedaugmentation material 920 and spacers 175 to the underlying hard masklayer 130. In certain embodiments, the etch may include oxygen and ahalide species. A suitable etch chemistry includes O₂, He, and CHF₃. Asnoted above, suitable etch conditions, including bias voltages, willvary depending on the etching system, chemistries, deposited materials,and etch conditions used. In some embodiments, the RF power is in therange from about 200 W to about 1000 W and the RF bias voltage is in therange from about 0 V to about 300 V.

Advantageously, the resulting spacers 175 have a desired spacing, whichcan be exceptionally uniform or non-uniform to a desired degree in someembodiments. In some embodiments, the spacers 175 can be used fordefining a pattern in the substrate 110, directly, without anyintervening masking levels. In other embodiments, the pattern formed bythe spacers 175 can be transferred to one or more masking levels beforebeing transferred to the substrate 110.

In some other embodiments as seen in FIGS. 13A and 13B, the spacers 175are combined with another mask pattern before being transferred to thesubstrate 110. For example, a planarization material 210 can bedeposited around the spacers 175 and the planarization material 210 canbe patterned to form a combined pattern with the spacers 175. Aselectively definable material 220 can be deposited over theplanarization layer 210. The selectively definable material 220 can thenbe patterned to form a second pattern 230 in a level above the spacers.For example, the selectively definable material 220 can be patterned byphotolithography to define features in a periphery of the partiallyformed integrated circuit 100. The second pattern is subsequentlytransferred to the planarization layer 210, thereby being consolidatedon the same level as the spacers 175, as shown in FIGS. 14A and 14B. Inother embodiments, the planarization material 210 can be a selectivelydefinable material 220 such as photoresist, including positive ornegative photoresist. The photoresist is then patterned to form thesecond pattern on the same level as the spacers 175. The combinedpattern formed by the patterned planarization layer and the spacers 175can then be transferred to underlying layers or directly to thesubstrate 110. In some other embodiments, a pattern is formed by etchingan underlying hard mask layer using the spacers 175 as a mask and aplanarization material is deposited about the features formed in theunderlying hard mask layer, thereby allowing those features to beprocessed and combined with a second pattern as discussed above for thespacers 175. Suitable methods for forming the second pattern incombination with spacers can be found in. e.g., U.S. patent applicationSer. No. 11/214,544, filed Aug. 29, 2005.

With reference to FIGS. 15A and 15B, the spacer pattern 177 istransferred to the hard mask layer 130. The pattern transfer may beaccomplished by, e.g., anisotropically etching the hard mask layer 130.

With reference to FIGS. 16A and 16B, the pattern 177 is transferred tothe primary mask layer 140. The pattern transfer may be accomplished by,e.g., anisotropically etching the primary mask layer 140. With referenceto FIGS. 17A and 17B, the pattern 177 is transferred to the substrate110 using an anisotropic etch with the layer 140 acting as a mask forthe etch.

With reference to FIGS. 18A and 18B, the spacers 175 and mask layers 130and 140 overlying the substrate 110 are removed. Pitch multiplied lines310 are formed in the substrate 110. As seen in FIGS. 15A-18B, the innerand outer space balancing of the spacers transfers to the hard masklayer 130, the primary mask layer 140, and the substrate 110, such thatthe inner 830 and outer spaces 840 are substantially equalized.Advantageously, the resulting features have exceptionally uniformspacing as shown in the SEM of FIG. 19.

Example 1

Silicon oxide spacers were augmented by deposition of a polymer in areaction chamber of a 2300 Versys Kiyo from Lam Research Corporation ofFremont, Calif., United States. CF₄ and CH₂F₂ were flowed into thereaction chamber. The CF₄ was flowed at about 40 ccm and the CH₂F₂ wasflowed at about 80 sccm. The substrate temperature was about 50° C. andthe reaction chamber pressure was about 40 mTorr. The TCP power wasabout 500 W, the RF bias power was about 50 W and the RF bias voltagewas about 265V.

The polymer deposition resulted in polymer bridging. The depositedpolymer was etched to open the inner space. The etch chemistry includedHBr, O₂, and He. The HBr was provided to the reaction chamber at a flowrate of about 90 sccm, the O₂ was flowed at about 60 sccm, and the Hewas flowed at about 120 sccm. The substrate temperature was about 50° C.and the reaction chamber pressure was about 5 mTorr. The TCP power wasabout 300 W, the RF bias power was about 0 W and the RF bias voltage wasabout 600V. Advantageously, the resulting spacers had a desirablynarrowed outer space.

Example 2

Silicon oxide spacers were augmented by deposition and etching of apolymer in a reaction chamber of a 2300 Versys Kiyo from Lam ResearchCorporation of Fremont, Calif., United States. CF₄ and CH₂F₂ were flowedinto the reaction chamber. The CF₄ was flowed at about 40 sccm and theCH₂F₂ was flowed at about 80 sccm. The substrate temperature was about50° C. and the reaction chamber pressure was about 40 mTorr. The TCPpower was about 500 W, the RF bias power was about 50 W, and the RF biasvoltage was about 265V.

The polymer deposition resulted polymer bridging. The deposited polymerwas etched to open the inner space. The etch chemistry included O₂, He,and CHF₃, provided to the reaction chamber. The O₂ was provided to thereaction chamber at a flow rate of about 60 sccm, the He was flowed atabout 120 sccm, and the CHF₃ was flowed at about 90 sccm. The substratetemperature was about 50° C. and the reaction chamber pressure was about15 mTorr. The TCP power was about 600 W, the RF bias power was about 0W, and the RF bias voltage was about 150V. Advantageously, the resultingspacers had a desirably narrowed inner space.

It will be appreciated from the description herein that the inventionincludes various embodiments. For example, certain embodiments of thepresent invention provide a method for integrated circuit processingincluding providing a plurality of spacers overlying a material,depositing an augmentation material onto the plurality of spacers, theaugmentation material bridging upper portions of pairs of neighboringspacers without bridging together upper portions of neighboring pairs ofspacers, etching the augmentation material to form a pattern ofaugmented spacers, and transferring the pattern to the underlyingmaterial.

Certain other embodiments of the present invention provide a method ofintegrated circuit processing including selectively forming anaugmentation material on an outer sidewall surface or an inner sidewallsurface of a plurality of spacers, forming a pattern in an underlyingmaterial wherein features of the pattern are derived from the pluralityof augmented spacers.

Certain embodiments of the present invention provide a method forpatterning a substrate, including determining dimensions of an inner andouter space of a plurality of spacers, depositing a polymer onto theplurality of spacers, selecting an etch power to etch the polymer toachieve a desired open space dimension between the augmented spacers,and forming a pattern in an underlying substrate, wherein features ofthe pattern are derived from features of the augmented spacers.

Certain embodiments of the present invention provide a method forintegrated circuit fabrication including providing a plurality ofspacers, each spacer having an outer sidewall and an inner sidewall, theouter sidewall having a curved upper portion, wherein the inner sidewallis vertically straight relative to the outer sidewall. One of the inneror outer sidewalls of each spacer are substantially selectivelylaterally expanded.

It will also be appreciated by those skilled in the art that variousomissions, additions and modifications may be made to the methods andstructures described above without departing from the scope of theinvention. All such modifications and changes are intended to fallwithin the scope of the invention, as defined by the appended claims.

What is claimed is:
 1. A method for integrated circuit fabrication,comprising: forming a memory array, wherein forming the memory arraycomprises: forming a plurality of free-standing spacers over asubstrate; selectively forming an augmentation material on one side ofeach of the spacers to form a plurality of augmented spacers; andforming a pattern in the substrate, wherein features of the pattern arederived from the plurality of augmented spacers.
 2. The method of claim1, wherein selectively forming the augmentation material comprisespreferentially depositing the augmentation material on the one side ofeach of the spacers.
 3. The method of claim 2, wherein the spacers areformed by lines of spacer material alternating with open spaces, whereinpreferentially depositing the augmentation material depositsaugmentation material predominantly on sides of the spacers definingalternating ones of the open spaces, the alternating ones of the openspaces constituting a first set of open spaces.
 4. The method of claim3, wherein preferentially depositing the augmentation material formsbridges of augmentation material across tops of neighboring spacersdefining a second set of open spaces alternating with open spaces of thefirst set, wherein the bridges block further deposition of augmentationmaterial into the open spaces of the second set of open spaces.
 5. Themethod of claim 4, wherein selectively forming the augmentation materialcomprises etching the bridge after depositing the augmentation material.6. A method for integrated circuit fabrication, comprising: providing aplurality of free-standing spacers over a substrate; selectively formingan augmentation material on one side of each of the spacers to form aplurality of augmented spacers; and forming a first pattern in thesubstrate, wherein features of the first pattern are derived from theplurality of augmented spacers.
 7. The method of claim 6, whereinproviding the plurality of free-standing spacers comprises: providing aplurality of mandrels; blanket depositing a spacer material on themandrels; anisotropically etching the spacer material to define spacerson sidewalls of the mandrels; and removing the mandrels to leave thefree-standing spacers.
 8. The method of claim 7, wherein providing theplurality of mandrels comprises performing photolithography, wherein themandrels are formed of photoresist.
 9. The method of claim 6, whereinselectively forming the augmentation material comprises depositing theaugmentation material on the spacers and selectively removing theaugmentation material from a side of each of the spacers.
 10. The methodof claim 9, wherein selectively forming the augmentation material formsa bridge of augmentation material across some pairs of neighboringspacers, and wherein selectively removing the augmentation materialcomprises etching the bridge.
 11. The method of claim 6, whereinselectively forming the augmentation material comprises depositing apolymer.
 12. The method of claim 11, wherein depositing the polymercomprises chemical vapor depositing the polymer using ahalogen-containing carbon precursor.
 13. The method of claim 6, whereinforming the first pattern in the substrate comprises selectively etchingthe substrate relative to the augmented spacers.
 14. The method of claim13, wherein forming the first pattern in the substrate furthercomprises, before selectively etching the substrate: depositing aprotective layer over the augmented spacers; patterning the protectivelayer to form a second pattern in the protective layer; andsimultaneously transferring the first and the second patterns to thesubstrate.
 15. The method of claim 14, wherein patterning the protectivelayer to form the second pattern comprises: depositing a photoresistlayer over the protective layer; defining the second pattern in thephotoresist layer; and transferring the second pattern from thephotoresist layer to the protective layer.
 16. A method for integratedcircuit fabrication, comprising: providing a plurality of spaced-apartspacers over a substrate, each spacer having exposed first and secondsidewalls on opposing sides of the spacer; selectively laterallyexpanding one of the first or second sides of the spacers relative tothe other of the first or second sides of the spacers; and subsequentlytransferring a pattern defined by the spacers to an underlying material.17. The method of claim 16, wherein selectively laterally expandingcomprises depositing mask material on the spacers.
 18. The method ofclaim 17, wherein selectively laterally expanding further comprisessubjecting the deposited mask material to an etch to selectively removethe mask material from a side of each of the spacers.
 19. The method ofclaim 18, wherein subjecting the deposited mask material to the etchcomprises performing the etch with a sufficiently low bias power to formfooters of the mask material in spaces between pairs of neighboringspacers.
 20. The method of claim 16, wherein subsequently transferringthe pattern comprises transferring the pattern to hard a mask layeroverlying a substrate.